Farmall 656 ---fixed the lean running issue!

[littlefarmer]

I've got a Farmall 656 gas tractor that I use for farming. Pulling a tandem disk, and also hauling wagons of grain.

Acquired it about four years. Since the beginning, I've had a problem with it running lean. Always had to keep the choke out about 1/2 to get it to run right. It seems plenty of others have had the same problem with these tractors.

I tried everything--rebuilding the carburetor, replaced it twice with a pro-rebuilt one, new gaskets on the manifold, making sure there was no problem with the fuel delivery. New spark plugs, distributor cap, installed electronic ignition, double checked timing. Checked compression and valve clearance. Even got rid of the shut-off solenoid and replaced it with a needle-type main jet adjustment. Nothing helped.

So, awhile back I'm looking at the original IH parts book for this tractor. Checking out the carburetor section. I noticed for the main jet, it specifies a #52 drill bit size.

Purchased a set of small numbered drill bits. I check-out the jet size, on my existing carb, and it won't take anything larger than a #55. (With numbered drill bits like this, as the number gets lower the bit gets larger).

So I take a chance, and drill-out the jet the next size larger (#54). And hey! The tractor runs noticeably better!. I go down to a #53---runs smoother yet!

I've finally drilled it out to the #52 size, as specified in the parts manual. Now it runs perfect under load. No sputtering. No fiddling with the choke.

I check both the previous rebuilt carburetor I got, and also the original one that came with the tractor. The jets are at #55 size.

So I am wondering---why do the rebuilt carbs and rebuild kits currently sold, have a three-sizes smaller main jet, than what is specified by IH? Is it because the OEM jets are NLA? And the remanufacturers just stick in whatever will fit? Despite knowing that it won't run right?

Wanted to post this out here for any others who have been having this problem. I've seen more posts on this subject from other Farmall owners on the Internet, with the same problem. I'm hoping my fix will help them also.

PS---I've also found it's important to use genuine 91 octane gas in these tractors! (This is the octane level that IH specifies for these engines). DO NOT run standard 87 octane! It caused performance issues for me!

 

[fastfarmall]

I bought a new one in of the fall 66, it was a good tractor and pulled good, the next spring uncle Sam called my brother used is some, and it would spit and sputer bad also,when i got home from Basic training,Memorial day weekend, long story short, in the fall of 1967,I traded it for a 806 diesel. so it was a blessing in disguise for me!

 

[pete 23]

The problem with rebuilt carburetors is the rebuilders do not check specs good enough. A lot of specs get changed by a service bulletin but part books have already been in print so it never shows up in a service manual.

IH went to listing engines separate from the tractors and that really gets to be mix and match. That 263 engine was used in a 560, 660, 706, 656 and some combines. The parts book is not clear as to which carburetor is for all the different applications.

Changing an air bleed or nozzle affects the main jet also so all things have to be balanced. I never worry too much about opening up a main jet a little just like you did . If you do happen to go a little too far, that adjusting needle valve will take care of it unless you go ape. All the older tractors that ran distillate you had to rely on the adjusting screw when going to gasoline because the main jet was larger. All later gasoline engines were supposed to be main jetted for maximum load and you screw the needle out of the way.


Changes in gasoline have affected the jetting of carburetors and of course there is really nothing to go by, just playing with the carbs.

Then, try to find main jets. Difficult and mostly made to be resized to fit application on those IH carbs.

 

[DeltaSteve]

A tractor that comes from high altitudes have smaller jets. Reason is less oxygen,therefore less gas.We are at 5000+ ft.My inlaws 'farm' at 8000 above.Our tractors run rich with standard jets.we also have to advance timeing a bit to compensate. Not too bad at 5000,but at 8000 the difference is significant to the point on some engines getting black sooted spark plugs. We have one H farmall that is really bad about that.Gunnison;San Louis Valley;South Park Colorado are just 3 examples of high altitude 'farming'

 

[the tractor vet]

Ya know tat there is a LOT more to tweaking qa carb the grabbing a drill bit and Boring with the big auger . Number drill bit size is NOT always what the jet size is . and y a NEVER just DRILL a carb jet ya REAM a jet then ya make mods to the discharge tube then the venture . Case in point here did you know that a # 54 JET is NOT a #54 drill it is real close to a #56 , but NOT perfect , a # 74 JET on a Holley is NOT a # 74 drill but between a 47 and a 48 . You removed the shut down Solenoid and replaced with a old screw jet , here you did nothing at all except remove the way to stop dieseling on a HOT engine . Once you turned the key on the pentall was retracted to FULL FUEL and the amount was controlled by the jet . . Ing timing is critical and yep you probably did run the timing and set it , BUT whaqt is the dist reallying doing thru the timing curve ???? You can bet your BIPPY it is NOT 100% dead on the money as springs get weak , pin ware weight piviot points ware and the curve is OFF . Not many of us old farts left now ah days that know how to work on a dist. and run a dist. strobe and see what it is doing and what it takes to to get it back in line let lone how to change and recurve it . 91 gas is close but NO CIGAR to the lowest of 93 that was to be used back when they were new and the 93 was the JUNK gas of the day . Ford back in the time frame of the 656 and 706=806 gas made two 390 2 BBl engines one was a reg fuel and would run somewhat on the cheap grades like Gulf Tane and Sunoco 190 if the ing timing was set dead on the money and it had the correct vac. advance , sometimes they got mixed up at the factory .l That regular fuel engine was a 9-1 compression ratio Then ya had the Premium fuel 2 BBl engine , that one was a 9.5 to 1 and it needed the 105 grade and people w2ere always coming in complaining about PIGGING , we would do qa check over on tune up spec.'s and all was where it was suppose to be , We had at that dealer ship we had a dyno and i would take the customer back and run there car on the dyno and sure enough it would Ping rattle and roll , Pop the fuel line off the tank and hook up to the fuel supply that we had that was 105 and run the car long enough to drain what was in the system from the pump to the carb and then lay into it and it performed like it was suppose to and you would show them the top of the air cleaner and it said right on the top 390 2 Bbl. Premium fuel and walk him around the shop or up to the show room and show him a REGULAR fuel 390 @ bbl engine and we would always get OH i did not know i have been running the CHEAP stuff , back then that amounted to about three cents to a gallon and the premium fuel 90 2 BBl got about a mile and a half to two MPG better then the reg, fuel on . Gas powered trucks built back then on the H D models ran Premium fuel with and 8 something to 1 compression ratio . You reg 330- 390 ran reg. gas BUT the 331-391-477-and 534 ran HIGH TEST . Back then at the fuel stops the truck fuel islands had what was called TRUCK GAS and out ft. at the car islands they had the reg grade of 95 octane and the hightest came from the tanks that fed the trucks with 105 or better depending on supplier . You young pups do not know this . I learned this way back since i was one of them nut cases that liked to go fast . My first car was made to go fast faster then what it came from the factor and for her day she was right up there with the 292 four bbl and it required high test when new and that was back in 56 , then i added the 312 blower heads dual four bbl.s and Isky 3/4 cam the dual points the headers and made it go faster and back then i was buying High test TRUCK gas for 16.9 cents a gallon and also was getting 3 cents off buy usen the company name and paying cash . The company had a bunch of Gas powered semi tractors . The Mack that i started driving pulling a 50 ton Rodgers lowboy was gas powered when i first started driving it , BIG 6 cylinder gas with a four bbl carb , three MPG . and carried just enough fuel on it to make the run to the new job site with out stopping on the way down hauling the D 8's and even the New D9 G . Nope you were not going to set any land speed records , Dragging up then hills as low as 8-10 MPH easing down the other side so not to smoke the brakes . 11 hours or so to go 287 miles . Get a Motel spend the night and make the run home and do it is less then seven hours . Back in those days everybody had gas powered except the BTO 's The man i worked for had two large farms for the day around here and had a raft of tractors and only two were diesel powered , my uncle farmed a lot of ground and till 59 only had one diesel the rest were gas.